Results of the GAMs (final models) for the two separated time periods (1976–1993 and 1994–2014). The generalized cross validation (GCV), the deviance explained (Dev. Expl.) and the number of observations (n) are indicated. For each predictor, the degrees of freedom (d.f.), the significance value (p) and the deviance explained by the model excluding the corresponding predictor (Difference Dev. Expl. %) are provided. Predictors without statistics indicate that they were excluded by the backward stepwise model selection.